The invention concerns a flow cell with at least two inlet channels, each connectable with a reservoir and controllable by means of valves and ending in an inlet chamber, and a common discharge channel.
Flow cells of this kind are, for example, known in the shape of micro systems from the chemical analysis technique. This concerns planar micro systems, having substrates of glass, silicium, plastic or the like. These systems are also known under the name xe2x80x9cLab on a chipxe2x80x9d. They have built-in micro-valves, channels for fluid transport are available, reservoirs for fluid are provided, etc. The channel structure can be produced by etching, milling, boring, die-casting, hot embossing etc.
In this connection it is disadvantageous that the latest transported fluid always remains in the chamber, where it pollutes the next fluid to be transported. Therefore, rather long dead times have to be accepted, before an analysis can be made with the new fluid. Additionally, the first mentioned fluid remains in corners and dead spaces, so that a complete removal is difficult. This is particularly the case, when more than two inlet channels are required.
In an infusion arrangement as shown in U.S. Pat. No. 5,431,185, it is known to add drugs to the infusion solution via three inlet channels being controllable by valves. Pollution cannot take place here, as the continuously incoming infusion solution acts as rinsing fluid.
The invention is based on the task of providing a flow cell as mentioned in the introduction, in which the pollution risk is drastically reduced and the dead time until the new fluid is available in pure condition is substantially reduced.
According to the invention, this task is solved in that each of the two ends of the inlet chamber is connected with the discharge channel via an outlet channel.
New incoming fluid flows to both outlet channels and therefore press all rests of the old fluid via the ends of the inlet chamber and the outlet channels to the discharge channel. The new fluid, no matter from which inlet channel it flows in, is therefore rinsing medium for the old fluid. The dead time until the passing of pure new fluid is short. Inlet chamber and outlet channels can easily be dimensioned so that no dead spaces occur.
It is advantageous that the inlet chamber has a width, which is small in comparison with the length measured between the ends. The new fluid therefore flows closely past the ends of the other inlet channels in the inlet chamber, which gives a good cleaning effect. If possible, the width should be less than ⅕, preferably less than {fraction (1/10)} of the length.
It is also recommended that the last section of each inlet channel be formed by its valve. The new fluid therefore passes immediately by the closing member, which additionally improves the rinsing effect.
A particularly good effect occurs on a suitable choice of flow resistances of inlet chamber and outlet channels. Thus, it is recommended that the flow resistance of each outlet channel is at least equal to ⅕ of the flow resistance of the inlet chamber between its ends, and preferably at least equal to this flow resistance. In this connection, the flow resistance can be expressed in bar/(l/s), bar indicating the pressure, l the flow quantity and s the time. The desired flow resistances can easily be obtained through a selection of the cross section and the length of the outlet channels.
With regard to design, it is advantageous to have a chamber, which has on one side the inlet channels, on the other side the discharge channel and between these an island-like restriction element, which is limited by the inlet chamber and the two outlet channels. In this connection, the required chambers and channels can be planarly dimensioned, which in relation to three-dimensional embodiments simplifies the production and is particularly interesting to micro systems.
It is advantageous that the chamber and the restriction element are approximately rectangular. Such shapes are easy to produce and can be accurately dimensioned.
It is advantageous that the inlet chamber with the inlet channel ends and the outlet channels are arranged symmetrically to the connection of the discharge channel. This symmetry gives substantially the same conditions on cleaning the chamber by means of the subsequent fluid.
Additionally, it is possible without problems that at least three inlet channels end in the inlet chamber. Therefore, more than two fluids can optionally be available.
Further, it is expedient that the first section of the discharge channel is formed by a micro pump. Thus, the micro flow cell provided with a pump can be kept small.
A preferred opportunity comprises that four micro valves are connected with the inlet chamber. The length of the inlet chamber caused by this can be used for the length of the outlet channels or even for the arrangement of the micro pump andxe2x80x94subsequentlyxe2x80x94the two outlet channels.
Preferred is the use in a chemical micro analysis system. There are several opportunities to perform different measurings at relatively short intervals. For example, the micro flow cell is suitable for water analyses in sewage plant.